A new study sheds light on the ability of the Zika virus to infect and replicate in placental immune cells without killing them, which could explain how it travels through the placenta of pregnant women and makes its way into the brain cells in their fetuses.
"Our results substantiate the limited evidence from pathology case reports," said Mehul Suthar of the Emory University School of Medicine and senior author of the study. "It was known that the virus was getting into the placenta. But little was known about where the virus was replicating and in what cell type."
The team used cells from full-term placentae gathered from healthy volunteers who delivered via Cesarean section
During the course of the research, the team discovered that the Zika virus can infect placental macrophages in cell culture, as well as another type of placental cell called cytotrophoblasts, although it needs a couple of days to do so. Furthermore, the level of viral replication was found to vary by donor, suggesting that certain placentae might be more susceptible to the virus than others.
"Not every pregnant woman who is infected by Zika transmits the virus to her fetus," Suthar said. "Host genetics and non-viral factors, including nutrition and microbiota, as well as timing may be influencing infectivity. A better understanding of these factors could allow the design of preventive measures, and eventually antiviral therapies."
Other flaviviruses related to Zika - such as dengue, West Nile and yellow fever - rarely cross the placental barrier, making Zika unique and a focal point for current research on this family of viruses.
"Zika may be unique in its ability to infect placental cells and cross the placental barrier, in comparison with other flaviviruses," Suthar said.
The Emory University team plans to continue to investigate placental cells and their immunology using cells donated from humans as well as animal models in an attempt to determine how and why the Zika virus affects the fetuses of pregnant women.
"We need to answer questions such as: what are the receptors that allow the virus to enter Hofbauer cells," Suthar said. "Do these cells change in their immune status during the different phases of pregnancy?"
The findings were published May 27 in the journal Cell Host & Microbe.
